1. Technical Field
The present invention relates to a unit cell for a flat-tubular solid oxide fuel cell or solid oxide electrolyzer, and a flat-tubular solid oxide fuel cell and a flat-tubular solid oxide electrolyzer using the same.
2. Description of the Related Art
Typically, a fuel cell is a high-efficiency clean power generation technique which converts hydrogen contained in a hydrocarbon material such as natural gas, coal gas, methanol, etc., and oxygen in air into electrical energy via an electrochemical reaction. The fuel cell is classified into, depending on the kind of electrolyte used, an alkaline fuel cell, a phosphate fuel cell, a molten carbonate fuel cell, a solid oxide fuel cell, and a polymer fuel cell.
An electrochemical reactor such as a solid oxide fuel cell, a high-temperature electrolyzer, etc., is classified into a flat type and a cylindrical type, depending on the shape thereof. Although the flat type exhibits high power density (power), a gas sealing area is large and thermal shock occurs due to a difference in the coefficient of thermal expansion between stacked materials, making it difficult to achieve a large-area device. The cylindrical type is comparatively superior in terms of resistance to thermal stress and mechanical strength, and may achieve a large-area device via extrusion, but is problematic because its power density is low.
A flat-tubular electrochemical reactor such as a flat-tubular solid oxide fuel cell having advantages of both the flat type and the cylindrical type electrochemical reactors is disclosed in Korean Unexamined Patent Publication No. 2005-0021027 and U.S. Pat. No. 7,351,477. In order to increase power, the flat-tubular electrochemical reactor is provided in the form of a cell stack, but the total thickness of the cell stack comprising stacked unit cells may increase in proportion to an increase in the thickness of unit cell, undesirably making it difficult to reduce the size of a fuel cell.